The present invention relates to improvements in known air springs used for suspension of the chassis in heavy transport vehicles. Such air springs, which are generally connected between the chassis and the wheel axle, generally comprise a lower vessel, called a piston, made of a rigid, pressure-resistant material such as steel, and an upper bellows, mounted on the vessel, made of e.g. nylon-reinforced rubber and being in pneumatic connection with the piston.
Air springs are generally commonly used today for transportation vehicles of various sizes. Depending on the size and weight of the vehicle, from two up to eight air spring units generally used, which may be arranged in pairs on a bogie. The air pressure in these air springs is in the order of about 8 bar, and the air spring pressure is maintained by means of one or more valves in a piping system connected to a pressurized tank which receives its compressed air from a compressor, which, in turn, is driven by the vehicle engine. The same air spring principle is also used for the cab suspension.
Since the upper part of these air springs consist of a bellows, the top cover of the bellows, which faces upwards, and supports the chassis, will therefore generally be pushed upwards by a higher pressure, and will be lowered by a lower pressure. In this manner, the height of the vehicle above ground level may be controlled, and it is also possible to tilt the vehicle in relation to the ground by using different pressure levels in the air springs on different sides of the vehicle. An inclination of the vehicle towards one side, caused by an uneven load, may also be adjusted by using different pressure levels in the air springs on both sides of the vehicle.
A level regulator, which can sense and control the level of the vehicle in relation to the ground, is arranged on the chassis, and this regulator, which supplies air to and/or discharges air from the air springs, can sense the level of the chassis in relation to the wheel axle or the ground.
A major advantage of these air springs, besides having excellent suspension properties, is that the height of the vehicle above ground level can be adjusted. This allows the vehicle to be lowered, and to be adjusted to a correct height which is suitable for the height of a loading ramp, or to be run in under a trailer and then be raised, to carry the load to be transported. A simple electric control box for such lowering and raising is provided in connection with the driver""s cab, making it very simple for the driver to perform this raising and lowering operation.
In order to lower and raise the vehicle chassis by means of air springs, on the one hand requires that a large amount of air must be discharged to the environment when the chassis is lowered, and at the same time that air must be forced in again, from the pressurized air tank, when the chassis is raised. Since the amount of air under pressure, or to be pressurized, and which is accommodated in the air springs, is rather large, a substantial waiting time is required for the driver who wishes to lower or raise the vehicle, especially in the case of repeated height adjustments, e.g. when shunting several trailers or demountables, a waiting time that cannot be used for other activities. Particularly if the vehicle is without load and is to be lowered by its own weight, a rather long waiting time may occur. Consequently, there has for a long time existed a strong desire to reduce this waiting time.
In accordance with the present invention, this and other objects have now been realized by the invention of a method for adjusting the elevation of a vehicle chassis mounted on an air spring including a bellows and a rigid piston pneumatically connected to the bellows, the method comprising supplying pressurized air to the air spring, pressurizing the bellows in order to adjust the elevation of the vehicle chassis, and pneumatically isolating the bellows from the piston whereby the time for adjusting the elevation of the vehicle chassis is minimized by effecting the adjusting by pressurizing only the bellows. Preferably, the air spring includes a valve poppet movable between an open position and a closed position whereby the pneumatically isolating of the bellows from the piston comprises actuating the valve poppet to the closed position.
In accordance with one embodiment of the method of the present invention, the method includes providing the piston and the bellows with predetermined volume ratios whereby the amount of air required to adjust the elevation of the vehicle chassis is minimized.
In accordance with another embodiment of the method of the present invention, the method includes pressurizing the bellows only when the valve poppet is actuated to the closed position.
In accordance with the present invention, apparatus has also been discovered for adjusting the elevation of a vehicle chassis comprising an air spring including a bellows, a rigid piston pneumatically connected to the bellows, and a valve poppet movable between an open position and a closed position, whereby when the valve poppet is in the closed position the piston is pneumatically isolated from the bellows, and pressurizing means for pressurizing the bellows in order to adjust the elevation of the vehicle, whereby when the valve poppet is in the closed position the time for adjusting the elevation of the vehicle chassis is minimized by effecting the adjusting by pressurizing only the bellows.
In accordance with a preferred embodiment of the apparatus of the present invention, the piston comprises a pressure-resistant material, preferably steel.
In accordance with another embodiment of the apparatus of the present invention, the bellows comprises nylon-reinforced rubber.
In accordance with another embodiment of the apparatus of the present invention, the piston and the bellows have a predetermined volume ratio whereby the amount of air required for adjusting the elevation of the vehicle chassis is minimized.
In accordance with another embodiment of the apparatus of the present invention, the valve poppet is normally urged into the open position, but is activated into the closed position whenever the bellows is pressurized.
According to the present invention, an air spring for transport vehicles is provided, comprising a vessel (xe2x80x9cpistonxe2x80x9d) made of rigid, pressure-resistant material, such as steel, and a bellows fitted onto the vessel (xe2x80x9cpistonxe2x80x9d), made of e.g. nylon-reinforced rubber, being in pneumatic connection with the xe2x80x9cpistonxe2x80x9d and connected to a source of compressed air, the air spring being characterized by the xe2x80x9cpistonxe2x80x9d being provided with an air shut-off valve in the opening towards the bellows.
According to the present invention, the valve may consist of, or be located in, a partition wall between the xe2x80x9cpistonxe2x80x9d and the bellows.
The valve may, according to the present invention, consist of a rotary valve, which is closed and opened by a rotating motion.
According to the present invention, the valve may also consist of a seat/poppet valve, the poppet being raised and lowered by means of a piston in a separate cylinder inside the xe2x80x9cpiston,xe2x80x9d which is arranged to shut off the air inside the xe2x80x9cpiston,xe2x80x9d in a lowered position, while air is being discharged from or fed into the bellows, and to be open between the xe2x80x9cpistonxe2x80x9d and the bellows, in a raised position, when air is neither discharged from or fed into the bellows.